Southwest Sciences Inc

Flight tests of the VCSEL hygrometer on NSF's Gulfstream-V research aircraft.

NSF's Gulfstream V with VCSEL hygrometer (blue instrument on top of a/c)

Flight testing of Southwest Sciences VCSEL hygrometer is underway on NSF's High-performance Instrumented Platform for Environmental Research (HIAPER) Gulfstream-V aircraft operated by the National Center for Atmospheric Research. In the photo above, the VCSEL hygrometer can be seen as the blue instrument on the top side of the aircraft, slightly forward of the first passenger window. Mark Paige is presently leading the development and testing of this instrument.

Map of the the test flight from Boulder to the Gulf of Mexico. The flight path of test flight #4 took the aircraft from Boulder to the Gulf of Mexico and back, as shown on the map. The test flight included a number of bow ties around fixed points in the Gulf to resample the same air mass.

Instruments on the aircraft include Southwest Sciences VCSEL hygrometer and a chilled mirror dew/frost point hygrometer. The VCSEL hygrometer is based on laser spectroscopy of the free air stream. Time response is a fraction of second. The chilled mirror hygrometer has a slower time response as a result of the thermal mass of the mirror. This can be a problem when flying through regions of rapidly changing moisture.

A portion of the data from the two hygrometers is shown below. The VCSEL hygrometer is shown in red, the chilled mirror hygrometer is shown in blue, air temperature is shown in green and pressure (altitude) is shown in yellow. The moisture level is shown as the frost point temperature on the same left hand axis as the air temperature. There is generally good agreement between the two moisture instruments under steady-state conditions, but the VCSEL hygrometer has much better temporal/spatial resolution, rapidly reaching 100% relative humidity (humidity = frost point) as the aircraft flies through cloud layers, and recovering to the baseline without overshoot.

What's Next?

In October 2007 the instrument was shipped to Germany to participate in an intercomparison with other research-grade atmospheric hygrometers. Stay tuned for more results.

This project is currently under the direction of Mark Paige.

Contact Information

Southwest Sciences, Inc.
1570 Pacheco St., Suite E-11, Santa Fe, NM 87505
tel. (505) 984-1322/ fax (505) 988-9230



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